THE ROLE OF MACROPHAGES AND BONE-MARROW-DERIVED DENDRITIC CELLS IN THE REJECTION OF FETAL THYMUS ALLOGRAFTS

Deoxyguanosine (dGuo)-treated fetal thymus lobes are capable of prolon ged survival in histoincompatible recipients despite their expression of both class I and class II major histocompatibility complex (MHC) an tigens. Although dGuo treatment has been directly shown to eliminate l ymphocytes from the lobes its effect upon other marrow-derived passeng er cells such as macrophages and dendritic cells is less well defined. Here we show that dGuo-treated CBA (H-2k) fetal thymus lobes allowed to develop under the renal capsule of immunoincompetent BALB/c (H-2d) mice for 3 weeks are depleted of donor-type dendritic cells in contras t to grafts of untreated lobes where donor-derived dendritic cells are still detectable at this time. Moreover, dGuo-treated thymus lobes un derwent prompt allo-rejection if recolonized with donor-type dendritic cells prior to transplantation into immunocompetent recipients. Toget her with our observation that macrophages (or their precursors) surviv e dGuo treatment, these results suggest that the reduced immunogenicit y of fetal thymus grafts seen following dGuo treatment is related to d endritic cell, rather than macrophage depletion.